Boundary layer control (BLC) systems are well known to the prior art for improving or maintaining the lift provided to a fluid foil by fluid flow over surfaces of the fluid foil. Without boundary layer control, separation of the boundary layer of fluid from the fluid foil surfaces often occurs under certain conditions, decreasing the lift that would otherwise be available. Accordingly, boundary layer control systems function to limit or prevent such boundary layer separation by injection of a controlled fluid into the boundary layer, such as by directing a controlled fluid stream along the foil surface in the direction of fluid flow.
BLC systems find particular applicability in conjunction with short takeoff and landing (STOL) aircraft. Such BLC systems for aircraft commonly include a plurality of air injectors, such as a plurality of slots or nozzles, distributed spanwise along each wing ahead of an airfoil surface for which boundary layer control is to be effected. For example, the air injectors may inject controlled air at a tangent to the airfoil surface, with the size of each injector, and the spanwise location and orientation of the injectors, being chosen to obtain a stream of air spanwise along the wing.
Such BLC systems for aircraft have also included an air delivery apparatus for providing controlled air to the plurality of injectors. Typically, the air delivery apparatus takes high pressure bleed air from the compressor stages of the aircraft's jet engines and supplies it, through appropriate valves and ducting, to the plurality of injectors. Such high pressure engine bleed air is desirable to minimize the surface area of the injectors so that cruise performance of the aircraft is not adversely affected. However, the utilization of such bleed air poses problems in the design, manufacture and operation of BLC systems. For example, the prior art demonstrates BLC systems for aircraft in which both the injectors and the air delivery apparatus are fabricted as an integral part of the wing structure. Since the engine bleed air has associated therewith a relatively high temperature with respect to the ambient, large thermal stresses between the boundary layer system components and the remaining elements of the wing structure are encountered which have not been satisfactorily minimized by previous designs. Prior art BLC systems for aircraft also provide structure in which either or both of the injectors and air delivery apparatus are located external to the wing structure. While minimizing thermal stresses, such systems are disadvantageous with respect to those in which the boundary layer control system is an integral part of the wing inasmuch as the external structure introduces aerodynamic drag and therefore loses many of the benefits desired for boundary layer control.
Finally, the solutions afforded to the aforementioned thermal stress and aerodynamic problems which are incorporated in the BLC systems of the prior art typically result in apparatus which is expensive to manufacture and install.
It is therefore an object of this invention to provide an improved boundary layer control system for aircraft.
It is another object of this invention to provide such an improved boundary layer control system for aircraft in which the injectors and air delivery apparatus components thereof are integral with the wing structure to provide superior boundary layer control but which are designed to accommodate flexure of the wing structure and thermal expansion of the air delivery apparatus due to the use of high temperature, high pressure engine bleed air.
It is yet another object of this invention to provide such an improved boundary layer control system for aircraft which is inexpensive to manufacture and low in materials cost as compared with prior art boundary layer control systems.